Operational cycling voltage dependence of the oxygen vacancy distribution in 6 nm Hf0.5Zr0.5O2 ferroelectric capacitors

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We present a hard x-ray photoemission (HAXPES) study of the oxygen vacancy (VO) concentration profile in 6 nm Hf0.5Zr0.5O2 ferroelectric capacitors as a function of field cycling at three operational voltages, VOP, namely 1.5, 2.0, and 2.5 V. Pristine capacitors show a marked pinched hysteresis loop and a double peak I–V response consistent with domain pinning and/or an antiferroelectric phase. The capacitors are woken up by field cycling at all three VOP, as shown by the increase in remanent polarization 2PR and the partial merging of the ferroelectric switching current peaks. At higher VOP, fatigue sets in earlier. Non-destructive, synchrotron radiation-induced HAXPES was used to quantify the evolution of the VO concentration with cycling. Field cycling induces VO migration, unpinning domains during the ferroelectric wake-up with a concomitant reduction in coercive voltage with increasing VOP. The VO concentration profile is directly correlated with the internal field due to polarization, as evidenced by the Hf 3d binding energies. Above 105 cycles, there is evidence for additional VO generation, which can be associated with the onset of ferroelectric fatigue. Finally, imprint appears to be mainly due to charge injection with only a weak direct dependence on the VO concentration profile.

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